This invention relates to an apparatus for biaxial-blow-molding a hollow bottle-shaped container of a synthetic resin and a method of biaxial-blow-molding the same container.
A conventional biaxial-blow-molding apparatus for synthetic resin products is constructed to heat pieces or parisons of preformed injection molding articles molded in advance at a predetermined temperature, then associate the pieces in blowing molds, and to blow the pieces while orienting axially the pieces via orientation pins, thereby obtaining the products of desired shape.
However, the outer surface of the product thus blow-molded in the mold is substantially intimately contacted with the inner surface of the mold in the mold. Particularly when the product is heat treated such as a heat set in the mold, the bottom surface of the product is adhered to the inner bottom surface of the mold. Thus, this conventional molding of the product has in a disadvantage that it is difficult to smoothly remove the product from the mold.
In the conventional biaxial-blow molding, the orienting center of the bottom of the piece, with which the pin makes contact at the orienting time, is displaced so that the piece is formed in the unpreferable shape of a variety of shapes. This causes the blow-molded product to have an irregular thickness which is weaker in strength and poor in external appearance. In order to overcome this drawback and disadvantage, an orientation pin unit has been developed in which a bottom protruding pin for lightly holding the bottom of a piece or parison together with the end of the orientation pin is arranged along a rectilinear line of the orienting direction of the orientation pin to retract into the bottom of the mold while maintaining the holding state in synchronism with the displacing operation of the orientation pin, thereby preventing the displacement of the orientation pin of the bottom of the piece.